Project Summary/Abstract Systemic Sclerosis (SSc) can be a chronic life threatening autoimmune disorder associated with severe vascular damage and fibrosis of the skin and/or internal organs. Nevertheless, the factors that predispose individuals to the development of SSc, as opposed to other more common systemic autoimmune diseases such as SLE, remain ill-defined, and treatment options for patients afflicted with devastating forms of this disease are extremely limited. Intriguingly, although both SSc and SLE patients develop anti-nuclear antibodies (ANAs), each disease is associated with a distinct set of specificities that may reflect discrete aspects of tissue damage. Research in this area has been hampered by the lack of suitable animal models. We have recently developed a novel transgenic model that allows for the regulated expression of a pseudo- autoantigen on either MHC class II+ cells or on the vascular endothelium, and the potential for expression by other tissues known to be targeted in SSc. The overall goal of this application is to determine how specific T cell subsets and/or the microenvironment of pseudo-autoantigen expression influence the autoantibody repertoire and the clinical course of systemic autoimmune disease. The specific aims of the application are as follows: (1) Determine whether the autoantigens routinely associated with SSc can activate B cells and/or dendritic cells, and if so, whether they are preferentially released from tissues thought to be targeted by the immune system in SSc. (2) Determine how the functional capacity of pseudo-autoantigen- specific T cells influences the isotype and specificity of the autoantibody repertoire as well as the type of systemic autoimmune disease that is elicited in mice that systemically express the pseudo-autoantigen. (3) Determine how the microenvironment of pseudo-autoantigen expression influences the autoantibody repertoire and the type of systemic autoimmune disease that is elicited in mice by comparing the outcome of pseudo- autoantigen expression by MHC class II+ cells (conventional antigen presenting cells) to pseudo-autoantigen express by cells of the vascular endothelium. These studies will involve donor DO11 T cells, skewed to a Th1, Th2, or Th17 phenotype, and recipient mice that inherit (a) a tetracycline transactivator driven by either an invariant chain promoter or a vascular endothelial promoter and (2) a membrane-associated ovalbumin fusion protein whose expression is regulated by a tetracycline transactivator. T cells obtained from wildtype, lpr, or gld DO11 mice, will be included in the analysis since over-expression of FasL has been found to trigger a chronic fibrotic response in numerous experimental settings. Our results should provide important insights into the mechanistic basis of SSc and point to new therapeutic strategies for this devastating disease. Project Narrative: No proven treatment is currently available for many manifestations of Systemic Sclerosis (SSc), a devastating disease with significant morbidity and mortality. This study could lead to significant insights into the factors that trigger the development of SSc and strategies that might prove useful in limiting the progression of disease in afflicted patients.